Process control plants or systems often employ rotary valves, such as ball valves, butterfly valves, eccentric-disk valves, eccentric-plug valves, etc., to control the flow of process fluids. In general, rotary valves typically include a fluid flow control member disposed in the fluid path and rotatably coupled to the body of the rotary valve via a shaft. Typically, a portion of the shaft extending from the rotary valve is operatively coupled to a stem of an actuator (e.g., a pneumatic actuator, an electric actuator, a hydraulic actuator, etc.) of the rotary control valve.
In some instances, to be in compliance with standards created by regulatory bodies, such as the American Society of Mechanical Engineers, redundant blowout protection is added to valves to ensure that the shaft is retained within the valve body if a primary connection between the shaft and the fluid flow control member fails.
In some known examples, the redundant blowout protection includes a shaft having a step that engages a portion of a packing follower. However, removing material from the shaft to form the step decreases the structural integrity of the shaft. As a result, a fluid force against the fluid flow control member may twist and/or turn the shaft while an end of the shaft is held stationary, which enables fluid to flow through the valve even if the fluid flow control member is actuated to the closed position.
In other known examples, the redundant blowout protection includes a shaft having a groove that receives a snap-ring that engages a portion of a packing follower. However, depending upon the pressure requirements of the system, the interaction between the snap-ring and the portion of the packing follower may not retain the snap-ring within the groove if the primary connection between the flow control member and the shaft fails and, thus, this configuration is limited to relatively low pressure applications.